As is familiar, the quality of weld seams is checked by a radiographic procedure involving the X-raying of the seam and making a radiograph thereof. The film is developed and assessed as a documentary evidence of seam quality. Furthermore, other devices are available, by which the radiograph can be displayed on a closed-circuit TV set. However, this arrangement is usually not accepted as a document although the video display can be recorded on a magnetic tape and reproduced subsequently in the desired number.
However, none of these procedures ensures the determination of the true special image of the defect although e.g. a spherical inclusion is sometimes acceptable, but a flat sharp-contured one is not; both inclusions having the same radiographic image, both are graded as reparable.
Another point of relevance is the surface of seam to which the defect lies closer, from which the scraping is to be started for the subsequent correction. Thus there is an unequivocal need for exact data on the spatial location, size and configuration of weld defects. The currently known procedures are unfit for this purpose.
One object of our invention is the realization of a process, together with it's associated system, by which the spatial location, configuration and size of weld defects can be determined and which, furthermore, enable a quality control with documentary records.
Accordingly, our invention is a videographic process as procedure for the quality control of weld seams, involving the transillumination, point by point, of the weld seam of the test specimen with X-ray or gamma rays. Electrical signals are generated to represent the radiographic image of the weld and its surrounding. The radiograph is recorded and displayed simultaneously, the image is assessed, and the procedure is started all over again in the next point. The essential feature of the invention is the use of two radiation sources of identical intensity arranged symmetrically about the vertical axis, perpendicular to the longitudinal axis of the weld seam. The target plate of the video camera is arranged symmetrically to the vertical axes mention above, parallel to the longitudinal and the transversal exceeds in the area to be irradiated, in such a way that the axes of the radiation sources are aligned with the axis of the target plate. The first radiation source is operated in pulsed mode and the radiographic still picture obtained is converted into electric signals, and this first picture is stored away. Then the second radiation source is operated in a pulsed mode. The resulting picture is similarly converted into electrical signals, stored, and the two memorized images are compared each to a standard image recorded of a perfect weld of identical parameters previously recorded with this procedure. In the case of identity, the weld detail is graded flawless, whereas it is rejected if a difference is found.
The size of the first projected image on the transversal axis is determined in the first radiograph, the second projection of the defect being determine in the second one. Then the coordinates of the defect are computed as described below. ##EQU1## where L=half of the distance between radiation source,
M=height of radiation source above the weld, PA1 V=thickness of weld seam, PA1 .DELTA.'=distance of the target plate below the weld seam PA1 x'=the displacement of the first defect image from a given (Y) axis, PA1 x"=the displacement of the second defect image from the given (Y) axis. PA1 .DELTA.'=distance of target from the lower plane of the weld, PA1 V=thickness of weld, PA1 L=half-distance of radiation sources, PA1 M=elevation of the radiation source above the upper plane of the weld, PA1 g=thickness of weld, PA1 k=lower diameter of the irradiated space, PA1 G=upper diameter of the irradiated space, PA1 Y.sub.k =elevation of the intersection points of the conical ray beams above the weld, PA1 .DELTA.=elevation of the intersection points of the conical ray beams beneath the weld.
The defect coordinates obtained are noted, and so is the number of steps along the longitudinal axis as the third defect coordinate, and the test equipment is advanced by one step along the longitudinal axis parallel to itself. The steps of the procedure are repeated over and over again along the entire length of the weld.
Furthermore, our invention is embodied in a system for testing weld seams, involving a radiation source above the specimen carrying the weld, and a video camera under it. A picture display, a video storage and a computer (arithmetic unit) are attached to the video camera. The essential feature of the invention is the use of a second radiation source above the target specimen, the axes of the first and the second radiation sources and of the video camera coinciding in the same plane; they are secured to an actuation device, and the radiation sources are arranged symmetrically to the axis of the weld. Pointing downward at an angle, this arrangement complies with the formulae ##EQU2## where t=diameter of target plate,
Operated in pulsed mode, the radiation sources are connected to a control unit ensuring their alternating operation; a location signal source is connected to the actuation mechanism, the output of which is attached to the image storage, display and the arithmetic unit. Furthermore, it has a central control unit coordinating the functions of the subassemblies, with the outputs of the computer and the clock signal generator electrically connected to its inputs. The outputs of this central control unit are attached to the control inputs of the arithmetic unit, the radiation source control and the actuation device.
The equipment implementing our invention can be assembled practicably in such a way that the arithmetic unit includes a reference standard image storage, an image comparator, a provisional image storage ("latch"), a special-purpose computer, a data input unit and a defect storage. The video signal input of the arithmetic unit is connected to the signal inputs of the image comparator and provisional image storage; the output of the latter is connected to one data input of the special-purpose computer and to a signal input of the defect storage controlled by the special-purpose computer. The location signal input of the arithmetic unit is connected to the other data input of the special-purpose computer and to the other signal input of the defect storage; the output of the image comparator and the feedback output of the special-purpose computer are connected to the signal inputs of the central control unit. The control inputs of these units are connected to the control outputs of the central control unit; furthermore, the data input unit is connected to the basic data input of the special-purpose computer.